摘要:

AbstractA surface active pyrrole, which has a long hydrophobic chain attached to the 3 position of the pyrrole ring, is used to modify the surface properties of the pores of a porous, crosslinked polystyrene. The latter is prepared starting from a concentrated emulsion (an emulsion with a large volume fraction of the dispersed phase, here 0.81) of water dispersed in a continuous medium composed of styrene, divinyl benzene, a suitable surfactant, an initiator, and the surface active pyrrole. This modified crosslinked porous medium is emplyed as the host for a polypyrrole composite that is prepared first by imbibing the host with a solution of pyrrole and subsequently with an oxidant solution. The latter plays the role of catalyst for polymerization as well as the role of dopant. The presence of the head groups of 3‐alkyl pyrrole molecules on the surface of the pores of the host polymer increases the affinity of the surface for pyrrole. The improved wetting thus achieved for the pyrrole solution ensures a higher connectivity among the pyrrole films present on the internal surface of the host polymer and increases the conductivity of the polypyrrole composites by a factor of 2 to 14, depending upon the solvents employed for pyrrole and oxidan

ISSN:0021-8995    

DOI:10.1002/app.1991.070430701

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractA system of partial differential equations was developed to describe the transient, three‐step transport of moisture through packaged food products. The steps included (i) Fickian diffusion through the polymer package film; (ii) Langmuirian adsorption upon the food surface; and (iii) Fickian diffusion through the food material. A set of finite difference equations was derived to approximate the continuous model. These equations were solved for standard boundary conditions in each section of the food packages. The results can be used for the determination of the food package shelf lif

ISSN:0021-8995    

DOI:10.1002/app.1991.070430702

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractIn order to improve the separation characteristics of membranes for pervaporation, the introduction of fluoroalkyl groups into poly(1‐trimethylsilyl‐1‐propyne) (PTMSP) was achieved by two methods. First, 3,3,3‐trifluoropropyldimethylsilylated PTMSP was prepared via metalation of PTMSP followed by treating with 3,3,3‐trifluoropropyldimethylchlorosilane. About 6 mol % of 3,3,3‐trifluoropropyldimethylsilyl group was introduced by the polymer reaction. Second, the copolymerizations of 1‐trimethylsilyl‐1‐propyne (TMSP) with 1‐ (3,3,3‐trifluoropropyldimethylsilyl)‐1‐propyne (FPDSP) or 1‐ (1H,1H,2H,2H‐tridecafluorooctyldimethylsilyl)‐1‐propyne (FODSP) were carried out to afford TMSP/FPDSP or TMSP/FODSP random copolymers. The ratio of TMSP monomer unit and the comonomer unit,x/y, was in the range of 99/1‐85/15. All the chemically modified PTMSP membranes showed ethanol permselectivity for pervaporation of aqueous ethanol solution. In particular, the introduction of less than about 5 mol % of fluoroalkylsilylated units into PTMSP effectively enhanced the selectivity. However, excess introduction of FODSP comonomer unit caused a decrease of the selectivity, with the value being smaller than that of PTMSP membrane. Furthermore, tetrahydrofuran, acetone, acetonitrile, dioxane, and isopropanol were efficiently separated from their dilute aqueous solutions us

ISSN:0021-8995    

DOI:10.1002/app.1991.070430703

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractVarious azobenzene derivatives and polymers were attempted as materials for thin composite films containing a polymer, a liquid crystal, and lithium perchlorate which can undergo ionic‐conductivity switching induced by light or heat. Poly(vinyl chloride) ‐based composite films containing enantiotropic azobenzene liquid crystals1, exhibited significant ionicconductivity change based on thermo‐ and photoinduced phase transitions of1, the temperature dependence on the ionic conductivity reflecting the enantiotropic phase transition behavior of the liquid crystals. Marked, reversible ionic‐conductivity switching on alternating irradiation of UV and visible lights was attained with the composite films containing1, especially1(n= 12). Incorporation of monotropic liquid crystals3to the composite films allowed bistability in the temperature dependence on the ionic conductivity. Employment of a polycarbonate resin and poly(methyl methacrylate) as the polymer material of the composite films gave similar ionic‐conductivity changes to the poly(vinyl chloride) composite films, whereas polyethyleneoxide brought about some different results in the photoinduced ionic‐conducti

ISSN:0021-8995    

DOI:10.1002/app.1991.070430704

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractN‐(2‐hydroxypropyl) methacrylamide copolymers containing side chains terminated in a model ligand, N‐tert‐butyloxycarbonylglycine (Boc‐Gly), bound via photocleavable α‐methylphenacyl bonds were synthesized to test the possibility of developing an optically controlled ligand delivery system suitable for sensors. One of the copolymers was further covalently attached to 3‐aminopropyl triethoxy silane (APS) coated porous silica beads which were modified with an excess of α,ω‐diaminopoly(ethylene oxide), molecular weights 1000 or 5000. The photochemical release of ligand induced by exposure to light in solution and at the solid‐liquid interface was studied. The influence of solvent and the length of poly(ethylene oxide) (PEO) spacers on the rate of photocleavage were determined. The hydrolytic stability of the α‐methylphenacyl bond in both solution and at the solid‐liquid interfa

ISSN:0021-8995    

DOI:10.1002/app.1991.070430705

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe mechanical properties such as elastic modulus and stress‐relaxation and spin‐spin relaxation timeT2from pulse NMR were measured for surface‐oxidized carbon‐black‐filled natural rubber. The extent of reinforcement increased with CB volume percent in the range of 0–30%. At a given CB percent, this quantity increased by surface oxidation of fillers and decreasing filler size. From pulse NMR experiment, it was found that there were three components in rubber molecules which have different values forT2. Stress‐relaxation time and elastic moduli fitted one master curve against effective volume, fraction which is the sum of filler and bound rubber fraction. It was found that the distance between particle surfaces is the most important factor influencing reinforcing properties of fi

ISSN:0021-8995    

DOI:10.1002/app.1991.070430706

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractA series of suspension polymerizations of vinyl chloride monomer (VCM) was carried out in a 5‐L pilot plant reactor over the temperature range, 40–70°C. The reactor pressure and monomer conversion were monitored simultaneously every 7–8 min. The critical conversion Xf, at which the liquid monomer phase is consumed, was considered to occur when the reactor pressure fell to 98% of the vapor pressure of VCM for suspension at the polymerization temperature. The reactor model predictions of pressure are in excellent agreement with the experimental data over the entire conversion and temperature ranges studied. The mechanism of reactor pressure development for VCM suspension polymerization is discussed herein in some detail. For isothermal batch polymerization, the reactor pressure falls in two stages due to the effect of polymer particle morphology on pressure drop. The first stage is due to the volume increase of the vapor phase as a result of volume shrinkage due to conversion of monomer to polymer. The monomer phase is not yet consumed at this stage, but it is trapped in the interstices between primary particles creating a mass transfer resistance; therefore, the reactor pressure drops slowly. The second stage is due to both the volume increase of the vapor phase and to the monomer in the vapor phase diffusing into the polymer phase because of the subsaturation condition with respect to monomer in the polymer phase. The reactor pressure drops dramatically with an increase in monomer conversion at this stage. The present model can be used to predict reactor dynamics during suspension polymerization under varying temperature and pressure cond

ISSN:0021-8995    

DOI:10.1002/app.1991.070430707

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractResults from an experimental study of propylene polymerization in heptane diluent over a high activity Mg‐supported Ti catalyst are presented. The study provides an examination of the effect of operating conditions on polymerization rate, product melt index, and powder bulk density. Among the findings are that product bulk density decreases with increasing operating temperature and decreasing operating pressure while prepolymerization increases the bulk density. The results support the hypothesis that polymer morphology is closely linked to mass transfer limitations within the growing polymer particle during the early stages of polymerizatio

ISSN:0021-8995    

DOI:10.1002/app.1991.070430708

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe standard 90° peel test was modified in order to apply it to testing adhesion of thin polymer films to surfaces of silicon substrates, such as the silicon nitride passivation layer used in our solid‐state chemical sensors. The goal of this task was to develop a procedure for testing adhesion of both dry and wet films, which would yield repeatable, quantitative results quickly, and with simple sample preparation. It is important to produce valid comparisons of adhesion both over variations of a given polymer composition, and between films made of dissimilar polymer matrices. The method described herein could be applied to adhesion testing of a wide variety of thin polymer layers to solid surfac

ISSN:0021-8995    

DOI:10.1002/app.1991.070430709

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY

摘要:

AbstractThe individual, competitive, and displacement adsorption of polyvinyl alcohol (PVOH), hydroxyethyl cellulose (HEC), and hydroxypropylmethyl cellulose (HPMC) in aqueous solution onto an attapulgite clay has been systematically studied. For the individual adsorption experiments, the amount of polymer adsorbed at equilibrium decreased in the order PVOH, HEC, HPMC. In the competitive adsorption experiments, the adsorption level of each polymer is diminished by the presence of a competing polymeric species. Binary mixtures of a cellulosic polymer (HEC or HPMC) with PVOH result in a substantial reduction in the amount of cellulosic polymer adsorbed. In the displacement adsorption studies, the sequential addition of HEC or HPMC is not able to displace previously adsorbed PVOH molecules to any appreciable extent. However, the addition of PVOH to previously equilibrated HEC/clay or HPMC/clay suspensions results in a large amount of the adsorbed cellulosic polymer being displaced by PVOH, especially under conditions of high surface coverage. These results indicate that PVOH is preferentially adsorbed on the clay surface and the strength of attachment to the surface is greater for PVOH than for either cellulosic polymer.

ISSN:0021-8995    

DOI:10.1002/app.1991.070430710

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1991

数据来源: WILEY